This invention relates to a plastic material composed of silicon carbide powder and organo-silicon compounds; to the use thereof for producing shaped parts and semi-finished products, and to a process for producing ceramic articles.
It is known to coat shaped bodies with organo-silicon compounds in order to improve the corrosion resistance, heat resistance and oxidation resistance of these shaped bodies by a subsequent heat treatment.
The use of organo-silicon compounds as binders for silicon carbide powders is likewise known. DE-OS 3 007 384 describes the possibility of kneading silicon powder with a sintering aid and an organo-silicon polymer under the action of heat, and shaping this mixture by injection molding, and then baking it to form heat-resistant ceramic articles. In this case, polyborosiloxanes or polycarbosilanes which contain methyl groups and hydrogen as substituents on the silicon of the molecule skeleton are used as the organosilicon polymer.
A mixture of silicon carbide powder, an organo-silicon compound and a lubricant, selected from the group of the higher fatty acids, is known from DE-OS 3 409 385. This mixture can be shaped into moldings and sintered. In this case, the use of the lubricant is essential in order to impart to the mixture good flowability and improved mold-separation ability, because it is likewise known that mixtures of silicon carbide powder and an organo-silicon compound have low flowability. This means that such mixtures cannot be plastically deformed or the mixture remains adhering to the molds, even if the molds are coated with parting agents, so the molded articles are very often faulty. For this reason, mass production of molded products is difficult or impossible.
A further disadvantage of the known solutions is the low ceramic yield, since during the ceramic treatment e.g. the lubricant has to be burned out, which necessarily results in an increase in porosity.